The invention relates to a filter body of a fluid filter, especially an air filter.
German Utility Model DE 88 05 049 U1 discloses a filter body of the type defined above, having a filter element consisting of a folded filter material in the form of a cylindrical tube. Because of these folds or pleats, such a tubular cylindrical filter element is also known as a star filter. An end disk is usually attached to both of the axial ends of this filter element, thus forming a seal with a radial action. This seal comes to rest radially against a cylindrical sealing face in the case of a filter body inserted into a filter housing. This sealing face is usually provided on a connection of the filter housing which is arranged coaxially with respect fo the filter body and to which the filter body is attached or which is inserted into the filter body when at least one of the end disks is designed as an end disk that is open at the center.
Since the seals on the filter body act radially, for the filter body there is essentially the possibility of an axial adjustment within the filter housing. This axial adjustability is required, for example, to compensate for dimensional deviations due to tolerance between the filter housing and the filter body. Due to this axial adjustability, a certain relative movement between the filter body and the filter housing is possible in principle, but such movement is not desirable because it can have a negative effect on the sealing effect of the seals and because this relative movement can also lead to a problematical noise generation in operation of a vehicle equipped with these filters.
To prevent such a relative movement between the filter body and the filter housing, supporting means are mounted on the axial outside of the end disk with respect to the filter element and extend in a ring pattern there. These supporting means are designed with axial elasticity and in the case of a filter body inserted into the filter housing, they are in turn supported on a supporting contour which is designed on the filter housing and extends parallel to the end disk. Due to this support, there is an axial positioning of the filter body and the filter housing which suppresses relative movements between the filter body and the filter housing. Such supporting means may be designed in the form of a foam ring mounted on the end disk, for example.
However, it is relatively complicated and expensive to manufacture such a filter body, because in a first manufacturing step, the filter element is attached to one side of the end disk by means of a special joining technique, e.g. by plastification by means of ultrasound or by heating level softening, and in a second manufacturing step the supporting means must be attached to the other side of the end disk through a corresponding joining technique. In addition, an additional production step may be necessary to attached the seal to the end disk with a suitable joining technique. A simplification is obtained when the supporting means are already integrated into the end disk in the form of an annular collar at the time of production of the end disk, so that a joining method can be used for securing the supporting means. Since filter bodies are usually mass-produced products, eliminating a manufacturing step means a considerable economic advantage.
International Patent WO 97/41939 discloses a filter body in which the filter element is equipped with an open end disk on one axial end. On its radial inside edge, this end disk has an axial annular collar which forms a seal which acts radially. Between the annular collar and the filter element may be inserted a ring-shaped body which functions as a radial support for the annular collar.
British Patent 1,499,922 discloses a filter body whose filter element is equipped with end disks on its axial ends. Several sealing lips are molded on the end disks.
French Patent Application 1,186,929 A discloses a ring-shaped sealing element which is equipped with sealing lips that project axially. When installed, the sealing lips are deformed axially toward one another, thus producing a preliminary stress which creates the axial sealing effect.
Filter bodies of this type are relatively unstable and cannot be exposed to any especially great pressure differences.
The present invention is concerned with the problem of designing a filter body of the type defined in the preamble such that the expense required for its production are reduced.
Due to the inner frame proposed according to this invention, the stability of the filter body can be improved significantly. First, the filter element can be supported on the inner frame on the inside radially, so that the stability of the filter element with respect to radial pressure differences is increased. Secondly, the two end disks are supported axially on one another by means of the inner frame, so that forces acting axially on the filter body are transferred essentially not to the filter element but instead to the stable inner frame. Due to the increased stability, the filter body according to this invention has a longer lifetime and a broader spectrum of use.
According to an especially advantageous refinement of this invention, the annular collar which forms the supporting means as well as the end disk and the seal may all be designed in one piece as an injection-molded plastic unit, thereby also eliminating a joining operation for attaching the seal. The end disk designed in this way then need only be joined to the filter element and optionally to an inner frame to form a fully functional filter body.
In one refinement of this invention, the seal may be designed on the annular collar, thus yielding a design that is simple to manufacture. This variant can be improved upon especially expediently by having the seal and the annular collar work together in such a way that an increasing axial deformation of the annular collar causes an increasing radial adjustment of the seal in the direction of its radial sealing action. This has the result that axial distortion of the sealing body is associated with an increase in the preliminary tension on the seal and thus an improved sealing effect.
Other important features and advantages of the present invention are derived from the subordinate claims, the drawings, and the respective description of the figures with reference to the drawings.
It is self-evident that the features mentioned above and those to be discussed in detail below can be used not only in the combination given here but also in other combinations, or they may also be used alone, without going beyond the scope of the present invention.